Hot Rod Hauler

At the outset of our Hot Rod Hauler project, one of our major goals was to increase fuel economy while maintaining the towing capacity of our ’73 Ford F-350. And while we will be building a new fuel-injected engine in the near future to help meet that goal, the first step in our attempt at getting better mileage was the installation of an E40D overdrive automatic transmission from Gearstar Performance Transmissions.

The truck’s original C6 had been rebuilt, equipped with a shift kit and heavy-duty components. The Ford’s shortcoming was the 3.78:1 rear gears, which meant the 460 spins three-grand plus at highway speeds. What’s desperately needed is another gear and for that, there are basically three choices—converting to a manual trans with overdrive, adding an auxiliary overdrive unit to the existing transmission, or installing a contemporary overdrive automatic.

We ruled out the first option because of the difficulty and expense, plus we like the convenience of an automatic. And even though adding an auxiliary overdrive would provide taller gearing, the issue then becomes the torque converter. The reason lockup converters were added to contemporary overdrive automatics is that the increased load from the higher effective gear ratio causes the converter to slip. That not only reduces the gains made by the higher gear ratio in Fourth but also produces transmission-cooing heat, which dramatically shortens its life expectancy. The cure for this was the introduction of the lockup torque converter. However while slippage is eliminated, in many cases the torque capacity of the clutch pack in the converter is limited—as a result converter failures in trucks that are subjected to heavy loads and towing duty are a concern. Fortunately, Gearstar has addressed these issues by building their own torque converters. With additional heavy-duty clutch packs and premium internals, Gearstar’s triple-disc lockup converter has three times more capacity than stock.

Confident that there was a lockup converter that would do the job, the next step was to figure out which transmission to couple it to. Not surprisingly, there are a number of choices—Gearstar has adapters that allow the use of GM overdrives, the 700-R4, 4L60E and 4L80E are good candidates for an overdrive auto swap. Ford’s A0D and A0DE are also viable choices. Of course, the best bet is to talk to the experts at Gearstar and let them tailor a transmission to your particular needs. In our case, we chose the E40D.

For comparison, here are the gear ratios fo the C6 and popular overdrive automatics:

Ford’s replacement for the C6 was the E40D, which featured a fourth forward speed, electronic shift controls, and a lockup converter. Introduced in 1989, it was the Ford’s first fully electronic transmission. The E40D is a large transmission so it’s not a great candidate for all swaps; it’s 4-inches longer than a C6 and considerably larger in diameter with a big pan.

An unusual feature of the E40D is the shifter pattern, which is P-R-N-OD-2-1. In the (D) range, the transmission shifts through all four gears. A lockout button disables Overdrive operation allowing the transmission to shift through the first three gears only. Selecting 2 allows the transmission to shift from First to Second and holds it there, while 1 holds the trans in First.

As with all their transmissions, Gearstar makes modifications to the E40D based ont he application, and for heavy-duty towing, there’s a long list of improvements. Ours received a master overhaul kit with Alto hardened Kolene steels, Raybestos high energy, high heat frictions, Transgo heavy-duty reprogramming shift kit, high capacity five-plate forward clutch pack, direct six-plate clutch pack, intermediate four-plate clutch pack, overdrive three-plate clutch pack, steel overdrive planetary gear set, hardened drive shell, new kick down band, hardened input shaft, 45 element intermediate sprat, new overdrive sprag assembly, high volume pump assembly, six-pinion front planetary, roller-bearing center support, specially machined intermediate and overdrive pressure plates, updated solenoid pack, and an extra capacity aluminum pan with drain plug— and there’s probably a few other thins we forgot. The point is, this is one tough transmission that will get the job done for a long, long time.

When it came time to plug the E40D in place of the C6, there was some good news and some bad. The good news is this is the only Ford overdrive automatic that will bolt directly to big-block (385-series) engines; the torque converter fits the original flexplate, and the output shaft is the same diameter and spline count as the C6, so the driveshaft yoke fits. Now the bad news— this trans is four inches longer. The driveshaft has to be shortened, the transmission mount and the crossmember below the bellhousing have to be modified, the shift linkage requires modification, and in our case, the main gas tank had to be slid back in its mounts and some "massaging" of one end required.

In this installment of the Hot Rod Hauler, we’re going to show you what it takes to make the transmission swap. Next month we’ll take an in-depth look at the electronics required to make the new breeds of overdrive automatics shift for themselves.

On the left is our replacement E40D, on the right is the original C6—note the larger diameter of the new transmission. Fortunately most early pickups have room for a four-speed manual. which means a tall transmission hump.
	The first obstacle to overcome was interference between the gas tank and the transmission. The cure was to slide the tank back in the brackets and "reshape" the end of the tank.
Ford’s E40D is 4-inches longer than the C6, the rear mount is 4 inches to the rear as well.
	Surprisingly, the only interference with the truck’s underbody was the bracket used to mount the transmission in a rebuilding fixture. Since we don’t think that will be needed any time soon, we cut it off.
Tim Smith, hot rodder and machinist extraordinaire, dropped out the C6 then did the majority of the fabrication necessary to install the new gearbox.
	With the bracket removed and the gas tank moved back and modified, the transmission fit into the tunnel. Note the two long projections, they have threaded holes that will come in handy.
A rubber mallet was used to reshape the front of the gas tank—that modification provided the room necessary for the transmission case, the rear mount, and the speed sensor that cannot be seen from this angle.
	To simplify installation and removal of the new transmission, Tim cut the ends off the stock crossmember and added a removable center section made from square tubing. Gearstar provided the finned-aluminum, extra capacity pan.
When installing any automatic transmission there should be some space between the flexplate and the torque converter with the bellhousing tight against the block. That indicates the converter is properly seated in the pump. Once that is determined, the converter nuts can be installed and tightened.
	Shown here is the original transmission crossmember—the stock rubber mount bolted directly to it.
This is the crossmember that fits below the bellhousing; it had to be modified for transmission clearance.
	From the factory, the transmission crossmember sat on top of a pair of frame brackets and was secured with a single bolt on each side.
To accommodate the new transmission mount, Tim fabricated a new bracket and welded it to the crossmember.
	The modified crossmember now mounts to the bottom lip of the frame., to the rear of its original location.
	Our F-350 has a two-piece driveshaft, Drive Line Service of Eugene, Oregon took 4 inches out of the front section..
AS the shift lever on the E40D is much farther to the rear. Tim manufactured the linkage necessary to connect it to the rod that shifted the C6. He made a bracket that attaches to the two threaded bosses referred to earlier. It mounts an aluminum bellcrank that hooks to the rod from the column shifter.
	For the use of our truck, an effective transmission cooler is required, so wer opted for one with a fan.
From the bellcrank, a rod runs to the rear to and attaches to a custom aluminum gear-selector arm, also fabricated by Tim.
	Our choices for a cooler location were limited; there was no room behind the grille, so we made brackets to hang it in the air stream below the radiator. With the fan on, the cooler airflow shouldn’t be a problem.